Eyeglass prescriptions call for lenses having a specific combination of optical parameters that meets the needs of a particular person. The industry does not consider it to be practical to prefabricate a stock of lenses having every possible gradation of each parameter in every possible combination that may be needed. Consequently, a sizable proportion of eyeglass lenses are custom made at the facilities of dispensing opticians or optical laboratories.
Lenses have traditionally been formed as a single integral body of glass or plastic. Grinding or molding such lenses to meet the specifications of a particular prescription requires costly equipment, highly skilled technicians and is time consuming. It has been found that the fabrication of ophthalmic lenses can be economically accomplished in a more rapid manner with a laminated lens construction in which two lens wafers are bonded together with a transparent adhesive.
The laminate construction enables assembly of lenses having any of a large number of different combinations of optical parameters from a relatively small stock of prefabricated lens wafers of different configurations. Pairing of different combinations of the wafers can, for example, provide lenses having any of a large number of different powers as the power of the lens is the summation of the powers of the two wafers. Cylinder correction for astigmatism can be adjusted by an appropriate rotation of one wafer relative to the other prior to bonding of the wafers. Bifocal or multifocal wafers can be used when called for by the prescription and interlayers of light absorptive, light reflective or polarizing material can easily be provided between the wafers in the case of sunglasses or the like. Prior U.S. Pat. Nos. 3,877,798; 4,892,403 and 4,645,317 describe examples of the above discussed laminate lens fabrication techniques in more detail.
The fabrication of laminate lenses is subject to certain problems which have not heretofore been adequately addressed and resolved. There is a risk that eyeglasses may be inadvertently mis-assembled using an individual wafer itself rather than the bonded pair of wafers which constitute the desired laminate lens. The resulting eyeglasses may not provide the needed vision correction but this may not be apparent, at least immediately, to the person who receives and wears the eyeglasses. The individual lens wafer by itself may also be too thin to provide a desirable degree of impact strength.
The risk of such mis-assembly is enhanced where the simplicity of fabricating lenses by lamination techniques results in the work being performed by persons who lack the skills of a highly trained and experienced optical technician.
The present invention is directed to overcoming one or more of the problems discussed above.